ArticlePDF Available

Relationship between solar activity and Δ14C peaks in AD 775, AD 994, and 660 BC

June 2017
Radiocarbon 59(4):1-10

DOI:10.1017/RDC.2017.59

License
CC BY 4.0

Authors:

Junghun Park

Korea Institute of Geoscience and Mineral Resources

Show all 5 authorsHide

Since the AD 775 and AD 994 Δ ¹⁴ C peak (henceforth M12) was first measured by Miyake et al. (2012, 2013), several possible production mechanisms for these spike have been suggested, but the work of Mekhaldi et al. (2015) shows that a very soft energy spectrum was involved, implying that a strong solar energetic particle (SEP) event (or series of events) was responsible. Here we present Δ ¹⁴ C values from AD 721–820 Sequoiadendron giganteum annual tree-ring samples from Sequoia National Park in California, USA, together with Δ ¹⁴ C in German oak from 650–670 BC. The AD 721–820 measurements confirm that a sharp Δ ¹⁴ C peak exists at AD 775, with a peak height of approximately 15‰ and show that this spike was preceded by several decades of rapidly decreasing Δ ¹⁴ C. A sharp peak is also present at 660 BC, with a peak height of about 10‰, and published data (Reimer et al. 2013) indicate that it too was preceded by a multi-decadal Δ ¹⁴ C decrease, suggesting that solar activity was very strong just prior to both Δ ¹⁴ C peaks and may be causally related. During periods of strong solar activity there is increased probability for coronal mass ejection (CME) events that can subject the Earth’s atmosphere to high fluencies of solar energetic particles (SEPs). Periods of high solar activity (such as one in October–November 2003) can also often include many large, fast CMEs increasing the probability of geomagnetic storms. In this paper we suggest that the combination of large SEP events and elevated geomagnetic activity can lead to enhanced production of ¹⁴ C and other cosmogenic isotopes by increasing the area of the atmosphere that is irradiated by high solar energetic particles.

Δ 14 C (‰) between AD 721 and 820 in tree rings from sequoia in Sequoia National Park, California, USA, compared to Δ 14 C in Japanese cedar (Miyake et al. 2012). The California data include numerous duplicates prepared from the same rings: the A-E designations indicate the time order of treatment and measurement for different batches.

…

Δ 14 C in Siberia (Larch, Jull et al. 2014), California, USA (bristlecone pine, Jull et al. 2014), Japan (cedar, Miyake et al. 2012), Germany (oak, Usoskin et al. 2013), New Zealand (kauri, Güttler et al. 2015), Poland (Quercus, Rakowski et al. 2015) plus average values for California sequoia from this study.

…

Figures - available via license: Creative Commons Attribution 4.0 International

Content may be subject to copyright.

Available via license: CC BY 4.0

Content may be subject to copyright.

RELATIONSHIP BETWEEN SOLAR ACTIVITY AND Δ

C PEAKS IN AD 775,

AD 994, AND 660 BC

Junghun Park

•John Southon

*•Simon Fahrni

•Pearce Paul Creasman

•

Richard Mewaldt

Korea Institute of Geoscience and Mineral Resources, 124 Gwahang-no, Yuseong-gu, Daejeon 34132, Korea.

Keck/AMS Lab, 3327 Croul Hall, University of California, Irvine, CA 92697, USA.

Laboratory of Ion Beam Physics HPK, Otto-Stern-Weg 5, 8093 Zurich, Switzerland.

Laboratory of Tree-Ring Research, University of Arizona, 1215 E. Lowell Street, Tucson, AZ 85721-0045, USA.

California Institute of Technology, MC: 290-17, Pasadena, CA, 91125 USA.

ABSTRACT.Since the AD 775 and AD 994 Δ

C peak (henceforth M12) was ﬁrst measured by Miyake et al. (2012,

2013), several possible production mechanisms for these spike have been suggested, but the work of Mekhaldi et al.

(2015) shows that a very soft energy spectrum was involved, implying that a strong solar energetic particle (SEP)

event (or series of events) was responsible. Here we present Δ

C values from AD 721–820 Sequoiadendron giganteum

annual tree-ring samples from Sequoia National Park in California, USA, together with Δ

C in German oak from

650–670 BC. The AD 721–820 measurements conﬁrm that a sharp Δ

C peak exists at AD 775, with a peak height of

approximately 15‰and show that this spike was preceded by several decades of rapidly decreasing Δ

C. A sharp

peak is also present at 660 BC, with a peak height of about 10‰, and published data (Reimer et al. 2013) indicate

that it too was preceded by a multi-decadal Δ

C decrease, suggesting that solar activity was very strong just prior to

both Δ

C peaks and may be causally related. During periods of strong solar activity there is increased probability

for coronal mass ejection (CME) events that can subject the Earth’s atmosphere to high ﬂuencies of solar energetic

particles (SEPs). Periods of high solar activity (such as one in October–November 2003) can also often include many

large, fast CMEs increasing the probability of geomagnetic storms. In this paper we suggest that the combination of

large SEP events and elevated geomagnetic activity can lead to enhanced production of

C and other cosmogenic

isotopes by increasing the area of the atmosphere that is irradiated by high solar energetic particles.

KEYWORDS: 660 BC, AD 775, CME (coronal mass ejection), M12, solar energetic particles (SPE).

INTRODUCTION

The strongest peak of Δ

C, corresponding to the event of AD 775 (called henceforth M12), and

another peak in AD 993/4 were measured by Miyake (Miyake et al. 2012, 2013) using

Cin

annually resolved Japanese cedar tree-ring sequences, and M12 has been conﬁrmed by several

studies (Usoskin et al. 2013; Jull et al. 2014; Güttler et al. 2015; Rakowski et al. 2015; Büntgen

et al. 2016) including three that showed peaks with slightly different starting times. Data

from high-latitude Siberian and Altai (Jull et al. 2014; Büntgen et al. 2016) record the AD 775

peak but show a Δ

C rise beginning one year earlier, and Δ

C data in New Zealand kauri

(Güttler et al. 2015) indicate a peak delayed by half a year.

Numerous causes of M12 have been suggested and examined (Thomas et al. 2013), including a

supernova (Miyake et al. 2012), a gamma ray burst (GRB) (Hambaryan et al. 2013; Pavlov

et al. 2013), and a solar proton event, also known as a solar energetic particle (SEP) event

(Melott et al. 2012; Miyake et al. 2012; Thomas et al. 2013; Usoskin et al. 2013; Jull et al. 2014;

Mekhaldi et al. 2015.) However, all of these hypotheses have some weak points. If M12 was

caused by a supernova, a candidate supernova should exist, but observations spanning several

hundred years before AD 775 record no such event. Supernovae emit both high-energy particles

and gamma rays, but high-energy particles from supernova have sufﬁcient energy spread that

extended arrival times spanning at least 10 yr would be expected (Gehrels 2003; Dee et al. 2017)

*Corresponding author. Email: jsouthon@uci.edu.

Radiocarbon, Vol 59, Nr 4, 2017, p 1147–1156 DOI:10.1017/RDC.2017.59

article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.

org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium,

provided the original work is properly cited

https://www.cambridge.org/core/terms. https://doi.org/10.1017/RDC.2017.59

Downloaded from https://www.cambridge.org/core. IP address: 191.101.91.124, on 13 Dec 2017 at 11:50:57, subject to the Cambridge Core terms of use, available at

whereas M12 shows a sharp 1–2-yr rise. Gamma rays from supernova and gamma ray bursts

have a very short duration time, implying that a short

C peak could occur, but M12 con-

centrations of the cosmogenic isotope

Be measured in Antarctic ice are much too high to have

been produced by a GRB (Usoskin et al. 2013). Since no evidence exists for any Δ

C increase

due to an historical SEP event (Jull et al. 2014), any solar phenomenon associated with the M12

peak must have been extremely intense and/or was a much more proliﬁc producer of

C than

those in the instrumental record. However, comparison of M12

Be and

Cl data from polar

ice cores (Mekhaldi et al. 2015) show a larger percentage increase over the long term back-

ground for

Cl than

Be. This result is consistent with production from a ﬂux of relatively soft

spectrum of incoming particles (Webber et al. 2007) and hence supports a solar rather than

galactic cosmic ray origin for M12.

This study introduces new M12 related Δ

C data from sequoia tree rings in Sequoia National

Park together with German oak Δ

C values from 650–670 BC and published data (Reimer

et al. 2013) that span a Δ

C peak at 660 BC. Following an analysis and comparisons of our

data with the ﬁndings of earlier work, the possible causes and processes associated with the M12

peak are discussed.

SAMPLES AND METHODS

Dendrochronological single-year tree-ring samples for AD 721–820 were prepared in the

Laboratory of Tree Ring Research (LTRR) at the University of Arizona from sequoia

(Sequoiadendron giganteum) in Sequoia National Park, California, USA. Sequoia is an ever-

green, common in coastal and montane regions of northern California and is among the tallest

living trees on Earth. The tree used for this research had rings large enough to ensure that the

tested samples contained only material from the precise indicated year, and each ring was

subsampled perpendicular to the ring direction to contain an even representation of the year’s

growth. The samples were treated by acid-base-acid and burned to produce CO

, which was

reduced to graphite and measured at Keck-Carbon Cycle AMS in University of California,

Irvine, USA. Additional aliquots of some samples were prepared and measured independently,

especially for the decades preceding the M12 spike.

The German oak samples from Oberhaid in Bavaria, Germany, were also prepared as single-

year samples at the Institute of Botany, University of Hohenheim, Stuttgart, Germany, and

acid-base-acid treated before combustion and subsequent graphitization at Keck-Carbon

Cycle AMS.

RESULTS AND DISCUSSION

M12 Peak Analysis

The M12 Δ

C data for the sequoia are presented and compared with results of

Miyake et al. (2012) in Figure 1, while Figure 2 shows six published datasets related to M12 plus

results from the present work. Since the Northern Hemisphere (NH) growing season

is generally from April to September, the appearance time of M12 in NH datasets is recorded

here as AD 775.5 and if a Southern Hemisphere (SH) tree ring showing M12 grew from

October AD 774 to April AD 775, the appearance time of M12 is recorded as AD 775.0

(Güttler et al. 2015).

The M12s in ﬁve NH datasets appear in AD 775.5, but Siberian larch from 67°31′N (Jull et al.

2014) shows a rise of about 6‰(<two standard deviations) one year early in AD 774.5, with

1148 J Park et al.

https://www.cambridge.org/core/terms. https://doi.org/10.1017/RDC.2017.59

Downloaded from https://www.cambridge.org/core. IP address: 191.101.91.124, on 13 Dec 2017 at 11:50:57, subject to the Cambridge Core terms of use, available at

additional increase of 9‰in AD 775.5 and 2‰in AD 776.5. The kauri dataset from New

Zealand shows M12 appearing 6 months later than in the NH (Güttler et al. 2015), consistent

with differences in the NH and SH growing seasons.

Figure 1 Δ

C(‰) between AD 721 and 820 in tree rings from sequoia in

Sequoia National Park, California, USA, compared to Δ

C in Japanese

cedar (Miyake et al. 2012). The California data include numerous duplicates

prepared from the same rings: the A–E designations indicate the time order of

treatment and measurement for different batches.

Figure 2 Δ

C in Siberia (Larch, Jull et al. 2014), California, USA

(bristlecone pine, Jull et al. 2014), Japan (cedar, Miyake et al. 2012), Germany

(oak, Usoskin et al. 2013), New Zealand (kauri, Güttler et al. 2015), Poland

(Quercus, Rakowski et al. 2015) plus average values for California sequoia

from this study.

Solar Activity and Δ

C Peaks 1149

https://www.cambridge.org/core/terms. https://doi.org/10.1017/RDC.2017.59

Downloaded from https://www.cambridge.org/core. IP address: 191.101.91.124, on 13 Dec 2017 at 11:50:57, subject to the Cambridge Core terms of use, available at

For a more detailed comparison (Table 1) we deﬁne baseline and intensity values for M12. The

baseline is deﬁned as the 4-yr Δ

C average for AD 770.5–773.5 in the NH (the AD 774.5 point

is not used, due to the possible early Δ

C rise in AD 774.5 in the Siberian record) and that for

AD 771.0–774.0 in SH. The NH intensity value is deﬁned as the 5-yr average for AD 776.5–

780.5, (the AD 775.5 point is not used since some records show Δ

C still rising in AD 775.5)

and the average for AD 777.0–781.0 is used for the SH intensity value. The baseline and

intensity values in the present work are higher by 2.7 ±1.4‰and 3.1 ± 1.2‰than those of

Miyake et al. (2012) respectively, similar to most of the other NH data: whether this represents a

real geographic difference or simply an interlaboratory offset is presently unknown. The

baseline and intensity values from New Zealand are ~6‰lower than the European and U.S.

data, consistent with measured NH-SH offsets over the last two millennia (Hogg et al. 2013;

Reimer et al. 2013). Given the uncertainties for the M12 heights, the magnitude of the M12

spike is essentially identical for six of the seven records, and although the M12 height for the

bristlecone pine record is low, it is nevertheless within two standard deviations of the mean of

the other six datasets.

The early (774 AD) rise in the Siberian and Altai Δ

C data is difﬁcult to reconcile with

results from the 1960s, when high-yield Soviet atmospheric nuclear tests in Novaya Zemlya

(~74°N) in September–November 1961 and again in the latter half of 1962 produced very high

burdens of excess

C in the NH stratosphere (Feely et al. 1966). After each major injection,

measurements of atmospheric

in air samples from NH ground stations (Nydal and

Lovseth 1983; Levin et al. 1985) showed a sharp rise beginning in the early spring of the

following year and continuing through the entire NH growing season. By 1963 when the largest

C increases were observed, a large network of sampling stations extending from 78°N to 9°N

was in place (Nydal and Lovseth 1983) and recorded an essentially synchronous Δ

C rise for

all stations. Since no anomalous early high-latitude tropospheric

signal in a bomb peak

was observed, it seems unlikely that any of the mechanisms put forward to explain the M12

peak from a high latitude like Siberia’s could generate an equivalent early

C spike in biomass.

Hence, conﬁrmations are required from measurements at other high-latitude sites.

As Figure 2 shows, the M12 peak is delayed in New Zealand kauri, but the delay is consistent

with the differences in timing of the NH and SH growing seasons. Furthermore, whereas the

maximum SH tropospheric

C increase during the bomb spike was just 70% of mid-latitude

NH values (Manning et al. 1990), reﬂecting the fact that close to 100% of the input was

generated within the NH, the M12 amplitude in the kauri is ~90% of the mean of the NH

stations (Table 1), indicating that signiﬁcant

C production occurred in both hemispheres.

Table 1 Baseline and intensity M12 Δ

C values plus heights (=intensity-baseline) for datasets

shown in Figure 2 (see text for details).

Location Latitude Baseline value (‰) Intensity value (‰) M12 height (‰)

Japan 30°N –20.3 ±1.1 –5.2 ± 0.7 15.0 ± 1.3

Siberia 68°N –17.2 ± 1.8 –0.4 ± 1.6 16.8 ± 2.4

Germany* 50°N –18.1 ± 0.8 –1.4 ± 0.8 16.7 ± 1.2

Poland 50°N –21.1 ± 0.9 –2.7 ± 1.0 18.4 ± 1.4

California (bristlecone) 38°N –17.3 ± 1.8 –6.2 ± 1.4 11.1 ± 2.3

California (sequoia) 36°N –17.6 ± 0.9 –2.1 ± 1.0 15.5 ± 1.4

New Zealand 36°S –23.8 ± 0.8 –9.7 ± 0.7 14.1 ± 1.0

*Average of data from two laboratories (Usoskin et al. 2013)

1150 J Park et al.

https://www.cambridge.org/core/terms. https://doi.org/10.1017/RDC.2017.59

Downloaded from https://www.cambridge.org/core. IP address: 191.101.91.124, on 13 Dec 2017 at 11:50:57, subject to the Cambridge Core terms of use, available at

Large-scale stratospheric air transport is dominated by the so-called Brewer-Dobson

circulation (Butchart 2014) characterized by injection of tropospheric air into the stratosphere

in the tropics and subsequently by movement towards the winter pole and subsidence at high

latitudes, driven primarily by seasonally varying large-scale eddy motions that act to reduce

the mean zonal velocity of air parcels and thus induce a poleward drift (Holton et al. 1995).

Descending air in the winter polar vortex carrying a high burden of stratospheric tracers is

released near the tropopause when the vortex breaks up in the spring, and extratropical injec-

tion of stratospheric air into the troposphere peaks in mid-to-late summer (Stohl et al. 2003).

Hence in both hemispheres, tropospheric

concentrations in the years following the bomb

spike showed seasonal cycles, with Δ

C increasing through the spring and summer and

reaching a maximum near the end of the growing season (Nydal and Lovseth 1983; Levin et al.

1985; Manning et al. 1990).

The M12 radiocarbon (

C) was produced simultaneously in both hemispheres according to

globally measured data and the events occurred in both hemispheres are undoubtedly con-

ﬁrmed by

Be data from Greenland and Antarctic ice cores (Sigl et al. 2015). Based on this

situation, we infer that this occurred in the early months of 775 AD, at the end of the northern

winter. The timing was early enough (and sufﬁcient production was generated low in the stra-

tosphere) that the NH stations received high-

C air when cross-tropopause exchange occurred

in the NH spring and summer of 775 AD, and hence the signal was recorded in NH wood

produced in mid-year. However, the event took place in the end of SH summer so that little or

C was injected into troposphere in that hemisphere during the 774/775 AD austral growing

season, and the signal only appeared in the New Zealand kauri in the 775/776 AD ring, almost a

year after the production event.

The 660 BC Peak and Solar Activity

Figure 3 shows Δ

C data covering the period from 550 to 750 BC including single year

European oak results from this study. A sharp peak with a rise time of 3–4 yr and amplitude of

Figure 3 Single-year Δ

C data in German oak spanning the 660 BC peak

(this work) are shown together with single-year and decadal data from

IntCal13 (Reimer et al. 2013).

Solar Activity and Δ

C Peaks 1151

https://www.cambridge.org/core/terms. https://doi.org/10.1017/RDC.2017.59

Downloaded from https://www.cambridge.org/core. IP address: 191.101.91.124, on 13 Dec 2017 at 11:50:57, subject to the Cambridge Core terms of use, available at

10‰is present at 660 BC. Although the rise time of the 660 BC peak is longer than that of M12

and the height of the peak is lower, the peaks in several of the M12 records actually take 2 yr to

reach their maximum value (Figure 2), and we suggest that the two peaks were probably

produced by similar processes and more measurement of the 660 BC peak are needed for

conﬁrmation.

The Δ

C data in Figure 1 show a decreasing trend (~0.2‰/yr) from 721 to 774 AD and distinct

periodic variations of an 11-yr solar cycle [the Schwabe cycle, average variation is a few per mil

(‰)] are seen on both sides of the M12 peak (Güttler et al. 2015). This suggests that an interval

of several decades prior to M12 showed elevated solar activity, characterized by a strong solar

cycle and low

C production due to enhanced heliomagnetic shielding against galactic cosmic

rays. The decadal Δ

C data from 725 to 675 BC in Figure 3 also show a decreasing trend,

suggesting that the 660 BC peak was also preceded by a period of strong solar activity. Any

downturn in Δ

C immediately preceding the single-year AD 994 peak, which Miyake et al.

(2013) suggest is also similar to M12, was very small and short-lived at best, but we note that

this peak did occur within an interval of generally low Δ

C. Hence although additional

research and data are needed, there is some evidence suggesting that these short-lived Δ

peaks are correlated with intervals of strong solar activity, and the simplest explanation is that

all three have a common cause.

Solar Proton Events and Coronal Mass Ejections

Why could a relationship between strong solar activity and the Δ

C peaks exist? Mekhaldi

et al. (2015) have pointed out that the high

Cl/

Be ratios for the M12 and AD994 peaks in

polar ice are consistent with production by relatively low energy particles (tens to hundreds of

MeV) and hence point to SEPs rather than galactic cosmic rays (GeV energies) as the source.

SEP events occur more frequently during strong solar activity periods (Kurt et al. 2004), and the

probability for very intense SEP events increases concurrently. A hypothesized explanation for

M12 and similar Δ

C peaks is that the Earth was irradiated by particles from one or more SEP

events involving extremely intense particle ﬂuxes, preferably characterized by unusually harder

energy spectra than those of most SEP events. The lower energy SEP component is deﬂected by

Earth’s magnetic ﬁeld and cannot interact with the atmosphere except at the poles, but the high

energy tail of the energy spectrum may have contained a sufﬁciently high ﬂuence of protons to

generate the observed burden of cosmogenic isotopes. Recently, superﬂares from Sun-like stars

were observed with a thousand times the energy release of the largest ﬂares on our Sun,

although the life stage at which Sun-like stars make superﬂares and differences between the Sun

and Sun-like stars are still under debate (Maehara et al. 2012, 2015).

This is a popular theory (Miyake et al. 2012; Usoskin et al. 2013; Jull et al. 2014; Mekhaldi et al.

2015) but a potential problem is that it requires a SEP ﬂuence at least ﬁve times larger than for

any event recorded in the era of ground-based or satellite observations (Mekhaldi et al. 2015).

Therefore, we consider the fact that large SEP events are often also associated with large

geomagnetic storms (Li et al. 2006), which can have the effect of enlarging the area of the

atmosphere that is irradiated by solar energetic particles (Leske et al. 2001).

Here we suggest a possible solution to this difﬁculty, based on the association of SEPs with

coronal mass ejection events (CMEs). A CME occurs when magnetic disturbances on the Sun

lead to the violent ejection of a large volume of plasma into interplanetary space, in the form of

an expanding thick shell that can extend over angular ranges of 120ºor more, anchored at the

source region on the Sun. Since the velocities of fast CMEs can reach ~2500–3000 km/s, far

1152 J Park et al.

https://www.cambridge.org/core/terms. https://doi.org/10.1017/RDC.2017.59

Downloaded from https://www.cambridge.org/core. IP address: 191.101.91.124, on 13 Dec 2017 at 11:50:57, subject to the Cambridge Core terms of use, available at

greater than the ~350–750 km/s speed of the solar wind, a shockwave forms in front of the CME

and the shocked solar wind plasma and the CME itself both contain embedded magnetic ﬁelds

that interact and reconnect with the geomagnetic ﬁeld. Fast CMEs are almost always accom-

panied by solar ﬂares, but typically most of the associated SEPs are not from the ﬂare itself, but

are solar wind and suprathermal ions (mainly protons) and electrons accelerated to tens to

thousands of MeV by the expanding CME shockwave (Gosling 1993; Reames 1999). Since

protons at these energies outrun the shock, SEP arrival at the Earth typically begins 1–2 days

prior to the interaction of the shockwave and the CME with the geomagnetic ﬁeld. In the largest

events a reservoir forms in the inner heliosphere (Reames et al. 1997) and elevated particle ﬂuxes

may persist for a week or more.

The fastest CMEs can reach Earth in a day or less and if the ﬂare site is located near the central

meridian the geomagnetic storm can often commence while SEP intensities are near their

maximum. Examples include the August 4, 1972, and July 14, 2000, events, among the largest of

the space era. In addition, Gopalswamy et al. (2004) and Li et al. (2012) have shown that many

CMEs involving especially high ﬂuences of SEPs are twin events where a second CME erupts

within 24 hours of the ﬁrst. The

C production from the two events would add nearly linearly

(Melott et al. 2012). Additionally the passage of the initial shockwave leaves a region in its wake

that for several hours contains high densities of suprathermal particles and elevated levels of solar

wind turbulence. If a second shock arrives before the suprathermal decay, it had been suggested

that particles are apparently accelerated with greater efﬁciency, producing a hard SEP ﬂux that

will generate unusually large numbers of secondary neutrons and correspondingly high levels of

C. Gopalswamy et al. (2004) ﬁnd that the second of these two events is typically more intense by

a median value of ~7. Furthermore, if the ﬁrst CME and/or the shocked plasma in front of it

contain strong embedded southward-pointing magnetic ﬁelds, these southward ﬁelds reconnect

with the north-directed ﬁelds on the front side of the magnetosphere, releasing a large amount of

energy. The resulting magnetic storm acts to reduce the geomagnetic ﬁeld, so that when SEPs

accelerated by the second shock reach the neighborhood of the Earth, they may encounter greatly

reduced geomagnetic cutoffs and hence can reach an abnormally large fraction of the atmosphere

(Leske et al. 2001; Kress et al. 2010).

To our knowledge, this hypothesis of a synergy between unusually intense and high energy

SEPs and reduced geomagnetic shielding has not been considered in the derivation of particle

ﬂuences required to explain the M12 peak, but elements of it are certainly consistent with CME

and SEP observations. Twin CMEs occur relatively frequently (Li et al. 2012; Ding et al. 2013)

and multiple large events within a few days (often from the same active region) are common.

Gopalswamy et al. (2004) reported that most of the large SEP events originating from CME-

driven shock acceleration in 1997 to early 2002 were preceded by an earlier CME-driven shock

event originating from the same solar active region within 24 hours earlier. For example,

80 CMEs, numerous intense ﬂares, and ﬁve large SEP events occurred over a three-week period

in October–November 2003, the four largest from a single, very active region on the Sun

(Gopalswamy et al. 2005; Mewaldt et al. 2005). Furthermore, over several periods of some

hours within this sequence, the geomagnetic cutoff latitude for 19–27 MeV protons was reduced

from 65° to 50–55° (Kress et al. 2010), corresponding approximately to doubling of the fraction

of the atmosphere exposed to those particles. The Carrington Event of 1859 involved major

magnetic storms on August 28–29 and September 2–3, with auroras visible at geomagnetic

latitudes as low as 25° and 18°, respectively (Green and Boardsen 2006), suggesting that two

closely spaced CMEs interacted strongly with the geomagnetic ﬁeld. As noted by Jull et al.

(2014), there is no evidence for this event in the annual

C record, which at ﬁrst sight appears to

Solar Activity and Δ

C Peaks 1153

https://www.cambridge.org/core/terms. https://doi.org/10.1017/RDC.2017.59

Downloaded from https://www.cambridge.org/core. IP address: 191.101.91.124, on 13 Dec 2017 at 11:50:57, subject to the Cambridge Core terms of use, available at

challenge the hypothesis outlined above, but we have no information on the intensity, spectrum,

and duration of the SEP event and the conditions for efﬁcient particle acceleration leading to a

very hard energy spectrum may not have been met (Li et al. 2006).

CONCLUSION

New Δ

C data from AD 721–820 from sequoia tree rings of California, USA, are presented

and compared with the result of Miyake et al. (2012). The calculated M12 height of 15.5 ± 1.4‰

and the appearance time of AD 775 for M12 in our record are same to those of Miyake et al.

(2012). Based on the amplitude and timing of the corresponding peaks in other NH records and

in New Zealand kauri,

C spike production was a global event and probably occurred in the

late northern winter (January or February) of AD 775. Δ

C data from 550–750 BC from both

the present study and Reimer et al. (2013) show that a sharp 10‰peak with a rise time of 3–4yr

is present at 660 BC. Although the 660 BC rise time is longer than that of M12 and the height is

lower, both peaks appear during periods of strong solar activity, and the simplest explanation

for the 660 BC and AD 994 spikes and M12 is that all three have a common cause.

The high

Cl/

Be ratios for the M12 and AD 994 peaks in polar ice (Mekhaldi et al. 2015)

support a relatively soft energy spectrum, consistent with production by accelerated solar

particles rather than galactic cosmic rays, but the SEP ﬂuxes required are far larger than any of

those in the instrumental SEP record. However, if a southward-pointing magnetic ﬁeld asso-

ciated with an intense CME event reconnects with the geomagnetic ﬁeld, an unusually large

fraction of the atmosphere may be exposed to particles accelerated efﬁciently by the shock wave

associated with a closely following second CME (Li et al. 2012). The synergistic effects of

reduced geomagnetic cutoffs and hard SEP spectra could lead to unusually effective production

C and other cosmogenic isotopes, and hence the calculated values for the required particle

ﬂuences may be too large. In addition, the largest events often occur during a period of elevated

solar activity when elevated SEP intensities and geomagnetic storms can continue for weeks.

Evidence for sharp reductions in geomagnetic cutoff values during CMEs and for multi-CME

sequences leading to unusually efﬁcient particle acceleration does exist, but determining

whether this mechanism can provide a quantitative explanation for the observed

C spikes will

require detailed calculations in future studies.

ACKNOWLEDGMENTS

This study was supported by a research project funded by the Ministry of Science, ICT and

Future Planning of Korea. We are grateful for helpful and constructive comments from

F Miyake and F Mekhaldi. The work at Caltech was supported by NASA under NNX13A66G,

and subcontract 00008864 of NNX15AG09G, and by the NSF under grant AGS-1622487.

SUPPLEMENTARY MATERIAL

To view supplementary material for this article, please visit https://doi.org/10.1017/

RDC.2017.59.

REFERENCES

Büntgen U, Myglan VS, Ljungqvist FC, McCormick

M, Di Cosmo N, Sigl M, Jungclaus J, Wagner S,

Krusic PJ, Esper J, Kaplan JO, de Vaan MAC,

Luterbacher J, Wacker L, Tegel W, Kirdyanovet

AV. 2016. Cooling and societal change during

the late antique little ice age from 536 to

around 660 AD. Nature Geoscience 9:231–6. DOI:

10.1038/NGEO02652.

Butchart N. 2014. The Brewer-Dobson circulation.

Reviews of Geophysics 52:157–84.

1154 J Park et al.

https://www.cambridge.org/core/terms. https://doi.org/10.1017/RDC.2017.59

Downloaded from https://www.cambridge.org/core. IP address: 191.101.91.124, on 13 Dec 2017 at 11:50:57, subject to the Cambridge Core terms of use, available at

Dee M, Pope B, Miles D, Manning S, Miyake F. 2017.

Supernovae and single-year anomalies in the

atmospheric radiocarbon record. Radiocarbon

59(2):293–302. DOI: 10.1017/RDC.2016.50.

Ding L, Jiang Y, Zhao L, Li G. 2013. The

“twin-CME”scenario and large solar energetic

particle events in solar cycle 23. The Astrophysical

Journal 763:30.

Feely HW, Seitz H, Lagomarsino RJ, Biscaye PE.

1966. Transport and fallout of stratospheric

radioactive debris. Tellus 18(2):316–28.

Gehrels N, Laird CM, Jackman CH, Cannizzo JK,

Mattson BJ, Chen W. 2003. Ozone depletion from

nearby supernovae. The Astrophysical Journal

585:1169–76.

Gopalswamy N, Yashiro S, Krucker S, Stenborg G,

Howard RA. 2004. Intensity variation of large

solar energetic particle events associated with

coronal mass ejections. Journal of Geophysical

Research 109:A12105.

Gopalswamy N, Yashiro S, Michalek G, Xie H,

Lepping RP, Howard RA. 2005. Solar source

of the largest geomagnetic storm of cycle 23.

Geophysical Research Letters 32:L12S09. DOI:

10.1029/2004GL021639.

Gosling JT. 1993. The solar ﬂare myth. Journal of

Geophysical Research 98:18937–49.

Green JL, Boardsen S. 2006. Duration and extent of

the great auroral storm of 1859. Advances in Space

Research 38:130–5.

Güttler D, Adolphi F, Beer J, Bleicher N, Boswijk G,

Christl M, Hogg A, Palmer J, Vockenhuber C,

Wacker L, Wunder J. 2015. Rapid increase in

cosmogenic

C in AD 775 measured in New

Zealand kauri trees indicates short-lived increase

C production spanning both hemispheres.

Earth and Planetary Science Letters 411:290–7.

Hambaryan VV, Neuhäuser R. 2013. Galactic short

gamma-ray burst as cause for the

C peak in AD

774/5. Monthly Notices of the Royal Astronomical

Society 430:32–6.

Hogg AG, Hua Q, Blackwell PG, Mu N, Buck CE,

Guilderson TP, Heaton TJ, Palmer JG, Reimer

PJ, Reimer RW, Turney CSM, Zimmerman SRH.

2013. SHCal13 Southern Hemisphere calibration,

0–50,000 years cal BP. Radiocarbon 55(4):

1889–903.

Holton JR, Haynes PH, McIntyre ME, Douglass AR,

Rood RB, Pﬁster L. 1995. Stratosphere-

troposphere exhange. Reviews of Gephysics 33(4):

403–39.

Jull AJT, Panyushkina IP, Lange TE, Kukarskih VV,

Myglan VS, Clark KJ, Salzer MW, Burr GS,

Leavitt SW. 2014. Excursions in the

C record

at AD 774–775 in tree rings from Russia and

America. Geophysical Research Letters 41. DOI:

10.1002/2014GL059874.

Kress BT, Mertens CJ, Wiltberger M. 2010. Solar

energetic particle cutoff variations during the

29–31 October 2003 geomagnetic storm. Space

Weather 8:S05001. DOI: 10.1029/2009SW000488.

Kurt V, BelovQA, Mavromichalaki H,Gerontidou M.

2004. Statistical analysis of solar proton events.

Annales Geophysicae 22:2255–71.

Leske RA, Mewaldt RA, Stone EC, Rosenvinge TT.

2001. Observations of geomagnetic cutoff varia-

tions during solar energetic particle events and

implications for the radiation environment at the

space station. Journal of Geophysical Research

106:30011–22.

Levin I, Kromer B, Schoch-Fischer H, Bruns M,

Münnich M, Berdau D, Vogel JC, Münnich KO.

1985. 25 years of tropospheric

C observations in

Central Europe. Radiocarbon 27(1):1–19.

Li G, Moore R, Mewaldt RA, Zhao L, Labrador AW.

2012. A twin-CME scenario for ground level

enhancement events. Space Science Reviews 171:

141–60.

Li X, Temerin M, Tsurutani BT, Alex S. 2006. Modeling

1–2 September 1859 super magnetic storm.

Advances in Space Research 38:273–9.

Maehara H, Shibayama T, Notsu S, Notsu Y, Nagao

T, Kusaba S, Honda S, Nogami D, Shibata K.

2012. Superﬂares on solar-type stars. Nature

485:478–81.

Maehara H, Shibayama T, Notsu Y, Notsu S, Honda S,

Nogami D, Shibata K. 2015. Statistical properties

of superﬂares on solar-type stars based on 1-min

cadence data. Earth, Planets and Space 67:59.

Manning MR, Lowe DC, Melhuish WH, Sparks RJ,

Wallace G, Brenninkmeijer CAM, McGill RC.

1990. The use of radiocarbon measurements in

atmospheric studies. Radiocarbon 32(1):37–58.

Mekhaldi F, Muscheler R, Adolphi F, Aldahan A,

Beer J, McConnell JR, Possnert G, Sigl M,

Svensson A, Synal H-A, Welten KC, Woodruff

TE. 2015. Multiradionuclide evidence for the

solar origin of the cosmic-ray events of AD 774/5

and 993/4. Nature Communications 6:8611. DOI:

10.1038/ncomms9611.

Melott AL, Thomas BC. 2012. Causes of an

AD 774–775

C increase. Nature 491:E1–2.

Mewaldt RA, Cohen CMS, Labrador AW, Leske

RA, Mason GM, Desai MI, Looper MD, Mazur

JE, Selesnick RS, Haggerty DK. 2005. Proton,

helium, and electron spectra during the large

solar particle events of October–November 2003.

Journal of Geophysical Research 110:A09S18.

DOI: 10.1029/2005JA011038.

Miyake F, Nagaya K, Masuda K, Nakamura T. 2012.

A signature of cosmic-ray increase in AD 774–775

from tree rings in Japan. Nature 486:240–2.

Miyake F, Masuda K, Nakamura T. 2013. Another

rapid event in the carbon-14 content of tree rings.

Nature Communications 4:1748. DOI: 10.1038/

ncomms2783.

Nydal R, Lӧvseth K. 1983. Tracing bomb

C in the

Atmosphere 1962–1980. Journal of Geophysical

Research 88:3621–42.

Pavlov AK, Blinov AV, Konstantinov AN, Ostryakov

VM, Vasilyev GI, Vdovina MA, Volkovet PA.

2013. AD 775 pulse of cosmogenic radionuclides

Solar Activity and Δ

C Peaks 1155

https://www.cambridge.org/core/terms. https://doi.org/10.1017/RDC.2017.59

Downloaded from https://www.cambridge.org/core. IP address: 191.101.91.124, on 13 Dec 2017 at 11:50:57, subject to the Cambridge Core terms of use, available at

production as imprint of a galactic gamma-

ray burst. MNRAS 435:2878–84.

Rakowski AZ, Krapiec M, Huels M, Pawlyta J,

Dreves A, Meadows J. 2015. Increase of radio-

carbon concentration in tree rings from Kujawy

(SE Poland) around AD 774–775. Nuclear

Instruments and Methods in Physics Research B

361:564–8.

Reames DV. 1999. Particle acceleration at the sun and

in the heliosphere. Space Science Reviews 90:

413–91.

Reames DV, Kahler SW, Ng CK. 1997. Spatial and

temporal invariance in the spectra of energetic

particles in gradual solar events. The Astro-

physical Journal 491:414–20.

Reimer PJ, Bard E, Bayliss A, Beck JW, Blackwell

PG, Bronk Ramsey C, Buck CE, Cheng H,

Edwards RL, Friedrich M, Grootes PM,

Guilderson TP, Haﬂidason H, Hajdas I, Hatte C,

Heaton TJ, Hoffman DL, Hogg AG, Hughen

KA, Kaiser KF, Kromer B, Manning SW, Niu M,

Reimer RW, Richards DA, Scott EM, Southon

JR, Staff RA, Turney CSM, van der Plicht J.

2013. IntCal13 and Marine13 radiocarbon age

calibration curves 0–50,000 years cal BP. Radio-

carbon 55(4):1869–87.

Sigl M, Winstrup M, McConnell JR, et al. 2015.

Timing and climate forcing of volcanic eruptions

for the past 2,500 years. Nature 523:543–9.

Stohl A, Bonasoni P, Cristofanelli P, et al. 2003.

Stratosphere-troposphere exchange: A review,

and what we have learned from STACCATO.

Journal of Geophysical Research 108(D12). DOI:

10.1029/2002JD002490.

Thomas BC, Melott AL, Arkenberg KR, Snyder BR

II. 2013. Terrestrial effects of possible astrophysical

sources of an AD 774–775 increase in

C produc-

tion. Geophysical Research Letters 40:1237–40.

Usoskin IG, Kromer B, Ludlow F, Beer J, Friedrich

M, Kovaltsov GA, Solanki SK, Wacker L. 2013.

The AD775 cosmic event revisited: the Sun is

to blame. Astronomy & Astrophysics 552:L3. DOI:

10.1051/0004-6361/201321080.

Webber WR, Higbie PR, McCracken KG. 2007.

Production of the cosmogenic isotopes

Be,

Be, and

Cl in the Earth’s atmosphere by solar and

galactic cosmic rays. Journal of Geophysical

Research 112:A10106. DOI: 10.1029/2007JA012499.

1156 J Park et al.

https://www.cambridge.org/core/terms. https://doi.org/10.1017/RDC.2017.59

Downloaded from https://www.cambridge.org/core. IP address: 191.101.91.124, on 13 Dec 2017 at 11:50:57, subject to the Cambridge Core terms of use, available at

The timing of the ca-660 BCE Miyake solar-proton event constrained to between 664 and 663 BCE

Article

Full-text available

Aug 2024

Extreme solar energetic particle events, known as Miyake events, are rare phenomena observed by cosmogenic isotopes, with only six documented. The timing of the ca. 660 BCE Miyake event remains undefined until now. Here, we assign its occurrence to 664–663 BCE through new radiocarbon measurements in gymnosperm larch tree rings from arctic-alpine biomes (Yamal and Altai). Using a 22-box carbon cycle model and Bayesian statistics, we calculate the radiocarbon production rate during the event that is 3.2–4.8 times higher than the average solar modulation, and comparable to the 774–775 CE solar-proton event. The prolonged radiocarbon signature manifests a 12‰ rise over two years. The non-uniform signal in the tree rings is likely driven by the low rate of CO2 gas exchange between the trees and the ambient atmosphere, and the high residence time of radiocarbon in the post-event stratosphere. We caution about using the event’s pronounced signature for precise single-year-dating.

A rapid cosmic-ray increase in BC 3372-3371 from ancient buried tree rings in China

Preprint

Nov 2017

Cosmic rays interact with the Earth's atmosphere to produce

^{14}

C, which can be absorbed by trees. Therefore, rapid increases of

^{14}

C in tree rings can be used to probe previous cosmic-ray events. By this method, three

^{14}

C rapidly increasing events have been found. Plausible causes of these events include large solar proton events, supernovae or short gamma-ray bursts. However, due to the lack of measurements of

^{14}

C by year, the occurrence frequency of such

^{14}

C rapidly increasing events is poorly known. In addition, rapid increases may be hidden in the IntCal13 data with five-year resolution. Here we report the result of

^{14}

C measurements using an ancient buried tree during the period between BC 3388 and 3358. We find a rapid increase of about 9\textperthousand~ in the

^{14}

C content from BC 3372 to BC 3371. We suggest that this event could originate from a large solar proton event.

Absolute dating of the European Neolithic using the 5259 BC rapid C excursion

Article

Full-text available

May 2024

Abrupt radiocarbon (¹⁴C) excursions, or Miyake events, in sequences of radiocarbon measurements from calendar-dated tree-rings provide opportunities to assign absolute calendar dates to undated wood samples from contexts across history and prehistory. Here, we report a tree-ring and ¹⁴C-dating study of the Neolithic site of Dispilio, Northern Greece, a waterlogged archaeological site on Lake Kastoria. Findings secure an absolute, calendar-dated time using the 5259 BC Miyake event, with the final ring of the 303-year-long juniper tree-ring chronology dating to 5140 BC. While other sites have been absolutely dated to a calendar year through ¹⁴C-signature Miyake events, Dispilio is the first European Neolithic site of these and it provides a fixed, calendar-year anchor point for regional chronologies of the Neolithic.

RADIOCARBON VARIATIONS IN ANNUAL TREE RINGS WITH 11-YEAR SOLAR CYCLES DURING 1800–1950

Article

Apr 2024
RADIOCARBON

The results of radiocarbon variation studies observed in annual tree rings from the NW Pacific (USA Northwest) (Stuiver and Braziunas 1993) and Europe (England, Brehm et al. 2021; Slovakia, Povinec 1977, 1987) are reviewed with the aim of better understanding the 11-year radiocarbon cycle and possible impacts of solar proton events on ¹⁴ C levels in the atmosphere and biosphere. The average Δ ¹⁴ C amplitude in tree rings for the period of 1798–1944 was 1.3 ± 0.3‰, the average periodicity was 11 ± 1 years, and the average time shift between the sunspot numbers and Δ ¹⁴ C records was 3 ± 1 years. A new solar activity minimum (Gleissberg minimum, 1878–1933) has been identified in the Δ ¹⁴ C data sets from the NW Pacific and England, showing Δ ¹⁴ C excess of 7‰, comparable to the Dalton minimum (1797–1823). No significant changes in Δ ¹⁴ C levels were identified that could be associated with solar proton events during 1800–1950.

Climate Impacts of the Millennium Eruption of Changbaishan Volcano

Article

Full-text available

Jul 2024

The Millennium Eruption of Changbaishan Volcano is heralded as one of the largest explosive eruptions in the Late Holocene and produced huge quantities of tephra. The petrogeochemical method estimates that the Millennium Eruption emitted up to 45 Tg of sulfur into the atmosphere—more than in the Tambora eruption in 1815 CE, which caused “a year without a summer” across the Northern Hemisphere in 1816 CE. Despite such massive emissions, evidence for this eruption's climate impact in East Asia remains elusive. To explain this contradiction, this study used 67 high‐resolution tree‐ring‐width records from the Northern Hemisphere spanning the past two millennia, complemented by volcanic sensitivity experiments conducted with the Community Earth System Model. Results reveal a prevailing decreasing/negative trend in the proxy records during the potential eruption period, with 945 CE marking the most notable negative anomaly, suggesting that the Millennium Eruption likely occurred in 945 CE rather than 946 CE. Sensitivity experiments, corroborated by proxy records, demonstrate that the Millennium Eruption induced substantial negative temperature anomalies at middle and high latitudes, alongside an increase in Meiyu‐Baiu‐Changma precipitation in the middle and lower reaches of the Yangtze River and southwestern Japan and a decrease in precipitation in India, northern China, and the South China Sea in the first post‐eruption year. This study offers a novel perspective on the climate impact of the Millennium Eruption, reconciling previous discrepancies regarding its climate impact.

Dividing Time – An Absolute Chronological Study of Material Culture from Early Iron Age Urnfields in Denmark

Preprint

Full-text available

Nov 2023

Chronological frameworks based on artefact typologies are essential for interpreting the archaeological record, but they inadvertently treat transitions between phases as abrupt events and disregard the temporality of transformation processes within and between individual phases. This study presents an absolute chronological investigation of a dynamic material culture from Early Iron Age urnfields in Denmark. The chronological framework of Early Iron Age in Southern Scandinavia is largely unconstrained by absolute dating, primarily due to it coinciding with the so-called ‘Hallstatt calibration plateau’ (c.750 to 400 cal BC), and it is difficult to correlate it with Central European chronologies due to a lack of imported artefacts. This study applies recent methodological advances in radiocarbon dating and Bayesian chronological modelling, specifically a statistical model for wood-age offsets in cremated bone and presents the first large-scale radiocarbon investigation of regional material culture from Early Iron Age in Southern Jutland, Denmark. Dated material is primarily cremated bone from 111 cremation burials from three urnfields. The study presents absolute date ranges for 16 types of pottery and 15 types of metalwork, which include most of the recognised metalwork types from the period. This provides new insights into gradual change in material culture, when certain artefact types were in production and primary use, how quickly types were taken up and later abandoned, and distinguishing periods of faster and slower change. The study also provides the first absolute chronology for the period, enabling correlation with chronologies from other regions. Urnfields were introduced at the Bronze-Iron Age transformation, which is often assumed to have occurred c.530-500 BC. We demonstrate that this transformation took place in the 7th century BC, however, which revives the discussion of whether the final Bronze Age period VI should be interpreted as a transitional phase to the Iron Age.

The Role of Deposition of Cosmogenic Be for the Detectability of Solar Proton Events

Article

Full-text available

May 2024

The manifestation of extreme solar proton events (SPEs) in Beryllium‐10 (¹⁰Be) ice core data contains valuable information about the strength and incidence of SPEs or local characteristics of the atmosphere. To extract this information, the signals of enhanced production of cosmogenic ¹⁰Be due to the SPEs have to be detected, hence distinguished from the variability of the background production by galactic cosmic rays (GCRs). Here, we study the transport and deposition of ¹⁰Be from GCRs, using the ECHAM/MESSy Atmospheric Chemistry climate model, and discuss the detectability of extreme SPEs (similar to the CE 774/775 SPE) in ¹⁰Be ice core data depending on the ice core location, seasonal appearance of the SPE, atmospheric aerosol size distribution and phase of the 11‐year solar cycle. We find that sedimentation can be a major deposition mechanism of GCR generated ¹⁰Be, especially at high latitudes, depending on the aerosols to which ¹⁰Be attaches after production. The comparison of our results to four ice core records of ¹⁰Be from Greenland and Antarctica shows good agreement for both ¹⁰Be from GCRs and solar energetic particles (SEP). From our results we deduce that the location of detection and the season of occurrence of the SPE have a considerable effect on its detectability, as well as the aerosol size distribution the produced cosmogenic nuclides meet in the atmosphere. Furthermore, we find that SPEs occurring in the phase of highest activity during the 11‐year solar cycle are more detectable than SPEs that arise in the phase of lowest activity.

Dividing time—An absolute chronological study of material culture from Early Iron Age urnfields in Denmark

Article

Full-text available

May 2024
PLOS ONE

A 1179-yr (417–1595 CE) tree-ring oxygen isotope chronology for northern Japan validated using the 774–775 CE radiocarbon spike

Article

Full-text available

May 2024
RADIOCARBON

We present an annual-resolution, millennium-long tree-ring chronology for northern Japan. The chronology is based on 5309 measurements of tree-ring δ18O from 37 samples of Hiba arbor-vitae (Thujopsis dolabrata var. hondae). Although the exact geographical origin of 27 of the samples is unknown because they were extracted from excavated archaeological material, pattern matching of the tree-ring δ18O variations was robust among all 37 samples. The floating chronology constructed using all samples was cross-dated against a previously published δ18O chronology from central Japan, yielding a correlation coefficient of 0.26 (t = 9.0; p < 0.01), resulting in a temporal coverage of 417–1595 CE (i.e., 1179 yrs). The global 14C spike event at 774–775 CE was clearly recorded in the annual 14C data, which provides independent support for the dating of tree rings using oxygen isotopes. Furthermore, this δ18O chronology from northern Japan was used to successfully cross-date a wood sample buried during the “Millennium Eruption” of Baitoushan, which is located on the border between China and North Korea.

Radiocarbon chronology of Iron Age Jerusalem reveals calibration offsets and architectural developments

Article

Apr 2024
P NATL ACAD SCI USA

Reconstructing the absolute chronology of Jerusalem during the time it served as the Judahite Kingdom?s capital is challenging due to its dense, still inhabited urban nature and the plateau shape of the radiocarbon calibration curve during part of this period. We present 103 radiocarbon dates from reliable archaeological contexts in five excavation areas of Iron Age Jerusalem, which tie between archaeology and biblical history. We exploit Jerusalem?s rich past, including textual evidence and vast archaeological remains, to overcome difficult problems in radiocarbon dating, including establishing a detailed chronology within the long-calibrated ranges of the Hallstatt Plateau and recognizing short-lived regional offsets in atmospheric 14C concentrations. The key to resolving these problems is to apply stringent field methodologies using microarchaeological methods, leading to densely radiocarbon-dated stratigraphic sequences. Using these sequences, we identify regional offsets in atmospheric 14C concentrations c. 720 BC, and in the historically secure stratigraphic horizon of the Babylonian destruction in 586 BC. The latter is verified by 100 single-ring measurements between 624 to 572 BC. This application of intense 14C dating sheds light on the reconstruction of Jerusalem in the Iron Age. It provides evidence for settlement in the 12th to 10th centuries BC and that westward expansion had already begun by the 9th century BC, with extensive architectural projects undertaken throughout the city in this period. This was followed by significant damage and rejuvenation of the city subsequent to the mid-eight century BC earthquake, after which the city was heavily fortified and continued to flourish until the Babylonian destruction.

Causes of an AD 777-775 14C increase

Article

Full-text available

Jan 2012
NATURE

25 Years of Tropospheric 14C Observations in Central Europe

Article

Full-text available

Jan 1985
RADIOCARBON

A long-term mountain station series of tropospheric 14 C data for the period 1959 to 1984 is presented. This series is considered representative of the higher altitude 14 C level over central Europe. Even tree-ring 14 C levels from a rural ground level site in southern Germany are consistently lower (by Δ 14 C depression = −15‰ if compared with the mountain station summer average in atmospheric CO 2 ). The rural tree-ring series is considered to represent the additional continental Suess effect at ground level without local contamination. This Suess effect decreases gradually with the distance from the ground ( ie , source) level. We therefore estimate the additional continental Suess effect in the vegetation period to be Δ 14 C depression = −5‰ for the mountain station and −20‰) for a rural ground level site, respectively. Based on this assumption, yearly mean tropospheric 14 C levels corrected for fossil fuel contamination and representative of the Northern Hemisphere are provided for use in global carbon cycle models.

Cooling and societal change during the Late Antique Little Ice Age from 536 to around 660 AD

Article

Full-text available

Feb 2016

Climatic changes during the first half of the Common Era have been suggested to play a role in societal reorganizations in Europe1,2 and Asia3,4. In particular, the sixth century coincides with rising and falling civilizations1–6 , pandemics7,8 , human migration and political turmoil8–13. Our understanding of the magnitude and spatial extent as well as the possible causes and concurrences of climate change during this period is, however, still limited. Here we use tree-ring chronologies from the Rus- sian Altai and European Alps to reconstruct summer tempera- tures over the past two millennia. We find an unprecedented, long-lasting and spatially synchronized cooling following a cluster of large volcanic eruptions in 536, 540 and 547 AD (ref. 14), which was probably sustained by ocean and sea-ice feedbacks15,16 , as well as a solar minimum17 . We thus identify the interval from 536 to about 660 AD as the Late Antique Little Ice Age. Spanning most of the Northern Hemisphere, we suggest that this cold phase be considered as an additional environmental factor contributing to the establishment of the Justinian plague7,8, transformation of the eastern Roman Empire and collapse of the Sasanian Empire1,2,5, movements out of the Asian steppe and Arabian Peninsula8,11,12, spread of Slavic-speaking peoples9,10 and political upheavals in China13.

SHCal13 southern hemisphere calibration, 0-50.000 cal BP

Article

Full-text available

Jan 2013
RADIOCARBON

Multiradionuclide evidence for the solar origin of the cosmic-ray events of AD 774/5 and 993/4

Article

Full-text available

Oct 2015

The origin of two large peaks in the atmospheric radiocarbon ((14)C) concentration at AD 774/5 and 993/4 is still debated. There is consensus, however, that these features can only be explained by an increase in the atmospheric (14)C production rate due to an extraterrestrial event. Here we provide evidence that these peaks were most likely produced by extreme solar events, based on several new annually resolved (10)Be measurements from both Arctic and Antarctic ice cores. Using ice core (36)Cl data in pair with (10)Be, we further show that these solar events were characterized by a very hard energy spectrum with high fluxes of solar protons with energy above 100 MeV. These results imply that the larger of the two events (AD 774/5) was at least five times stronger than any instrumentally recorded solar event. Our findings highlight the importance of studying the possibility of severe solar energetic particle events.

Timing and climate forcing of volcanic eruptions for the past 2,500 years

Article

Full-text available

Jul 2015
NATURE

Volcanic eruptions contribute to climate variability, but quantifying these contributions has been limited by inconsistencies in the timing of atmospheric volcanic aerosol loading determined from ice cores and subsequent cooling from climate proxies such as tree rings. Here we resolve these inconsistencies and show that large eruptions in the tropics and high latitudes were primary drivers of interannual-to-decadal temperature variability in the Northern Hemisphere during the past 2,500 years. Our results are based on new records of atmospheric aerosol loading developed from high-resolution, multi-parameter measurements from an array of Greenland and Antarctic ice cores as well as distinctive age markers to constrain chronologies. Overall, cooling was proportional to the magnitude of volcanic forcing and persisted for up to ten years after some of the largest eruptive episodes. Our revised timescale more firmly implicates volcanic eruptions as catalysts in the major sixth-century pandemics, famines, and socioeconomic disruptions in Eurasia and Mesoamerica while allowing multi-millennium quantification of climate response to volcanic forcing.

Transport and fallout of stratospheric radioactive debris

Article

May 1966

The Use of Radiocarbon Measurements in Atmospheric Studies

Article

Jan 1990
RADIOCARBON

14 C measured in trace gases in clean air helps to determine the sources of such gases, their long-range transport in the atmosphere, and their exchange with other carbon cycle reservoirs. In order to separate sources, transport and exchange, it is necessary to interpret measurements using models of these processes. We present atmospheric 14 CO 2 measurements made in New Zealand since 1954 and at various Pacific Ocean sites for shorter periods. We analyze these for latitudinal and seasonal variation, the latter being consistent with a seasonally varying exchange rate between the stratosphere and troposphere. The observed seasonal cycle does not agree with that predicted by a zonally averaged global circulation model. We discuss recent accelerator mass spectrometry measurements of atmospheric 14 CH 4 and the problems involved in determining the fossil fuel methane source. Current data imply a fossil carbon contribution of ca 25%, and the major sources of uncertainty in this number are the uncertainty in the nuclear power source of 14 CH 4 , and in the measured value for δ 14 C in atmospheric methane.

Supernovae and Single-Year Anomalies in the Atmospheric Radiocarbon Record

Article

Aug 2016
RADIOCARBON

Single-year spikes in radiocarbon production are caused by intense bursts of radiation from space. Supernovae emit both high-energy particle and electromagnetic radiation, but it is the latter that is most likely to strike the atmosphere all at once and cause a surge in 14 C production. In the 1990s, it was claimed that the supernova in 1006 CE produced exactly this effect. With the 14 C spikes in the years 775 and 994 CE now attributed to extreme solar events, attention has returned to the question of whether historical supernovae are indeed detectable using annual 14 C measurements. Here, we combine new and existing measurements over six documented and putative supernovae, and conclude that no such astrophysical event has yet left a distinct imprint on the past atmospheric 14 C record.

Increase of radiocarbon concentration in tree rings from Kujawy (SE Poland) around AD 774–775

Article